The present invention relates to a process for at least one of drying and pre-heating, by at least one of entraining and fluidising, coal to be coked by means of one of a neutral and reducing heat-conveying gas which is partially recycled and maintained at temperature of substantially 250.degree. to 650.degree. C., in which process coal is introduced into one of a drying and pre-heating chamber by means of a device for introducing the coal at at least one of a known and controllable rate. The present invention also relates to a plant for carrying out the process.
Almost all metallurgical coke is manufactured in conventional coke ovens in which the charge is raised to a temperature of approximately 1,000.degree. C. On being discharged from the coke oven, the coke is generally cooled by extensive water spraying in a quenching tower. The sensible heat thus lost from the coke represents 40 to 45% of the heat employed to heat the coke furnaces, which is 550 to 600 therms per ton of dry coal charge. This is the most important item of heat losses in the heat balance of the coking process. Recovery of the sensible heat of coke by means of quenching using a dry method has been considered for a long time, the principle of this method being as follows. The hot coke is cooled by direct contact with inert gases circulating in a closed cycle. The sensible heat recovered by the gases is used to produce steam.
However, dry quenching processes have in general been critised for producing steam which is not usually utilised. The use of this heat in the actual coking plant would obviously be far preferable to installing turbines for generating electricity. The pre-heating of coal could be another application, as already described in German Pat. No. 453,464, and more recently in French Pat. No. 2,173,997 and its equivalents, German Pat. No. 2,304,541 and U.S. Pat. Nos. 3,843,458 and 3,728,230, which propose, for drying the coal, the use of a gas which is heated in a heat exchanger by quenching gas, when the latter has already supplied some of its heat to a steam generator.
In German Pat. No. 453,464, the heat exchange is incomplete. In the other aforementioned process, an attempt has been made to isolate the two quenching and heat-conveying gas circuits with a number of complex gas-gas and gas-liquid exchangers, by providing the heat to the coal in two separate drying and heating stages and by introducing steam condensers. However, if the already dried coal is brought into contact with gases at a temperature of more than 350.degree. C., the coal will then be adversely affected.
An object of the present invention is to avoid these disadvantages and to provide a new process and a plant for carrying out the process, which allow the temperature of the heat-conveying gas to be properly regulated and the sensible heat of the dry-quenching fumes of the coke to be properly utilised, while avoiding the introduction, into the quenching fumes, of steam which is likely to gasify the coke. A further object of the present invention is to ensure that in all circumstances heat is provided in the necessary quantity to the heat-conveying gas, that is to say to the coal to be dried and/or pre-heated, whilst making it possible to use the heat which is in excess in relation to that necessary, particularly if the latter is a small quantity or non-existent as a result of voluntary or accidental stoppage of the dryer and/or pre-heater. A further object is, again, to enable the two quenching and drying and/or pre-heating plants to be separated at any time to prevent breakdowns affecting one plant from affecting the other.